Fuji files are 12bit, there is currently no 14bit option which would make them even bigger. The difference in size is more or less how the information is compressed. Looks like fuji files are not compressed. Loss less comressed files are smaller and how I used to set my Nikon.

just a matter of compression. Yes, I found Fuji files tend to be excellent in term of noise, DR and overall sharpness (at least in LR 5 and with the lenses I have such as 18-55 kit and a bunch of R and M optics)

Looking through some test shots, I see the Fuji RAF files (XE1) tend to be around 25MB for ISO 200 and Olympus OMD ORF files tend to be around 15MB.

This doesn't make any sense, because they are both about 16MP. Also, the Fuji generally is a little less noisy.

Are ORF files compressed RAW (hopefully loss-less??) and Fuji un- or less-compressed? Is Fuji more bits?

Anyone know the answer?

As stated before, the RAF files aren't compressed. Several manufacturers do compress their raw files (losslessly, but lossy formats exist as well). One giveaway is that the RAF files are always the same size. Compressed raw files generally vary in size.

If you want to save space (a lot of space...), you can compress the RAF files on your computer. If on a Mac or any other Unix machine, use the program 'bzip2' (in the terminal). You can save up to 80%, depending on the scene. There are likely similar compression tools on Windows.

Looking through some test shots, I see the Fuji RAF files (XE1) tend to be around 25MB for ISO 200 and Olympus OMD ORF files tend to be around 15MB.

This doesn't make any sense, because they are both about 16MP. Also, the Fuji generally is a little less noisy.

Are ORF files compressed RAW (hopefully loss-less??) and Fuji un- or less-compressed? Is Fuji more bits?

Anyone know the answer?

As stated before, the RAF files aren't compressed. Several manufacturers do compress their raw files (losslessly, but lossy formats exist as well). One giveaway is that the RAF files are always the same size. Compressed raw files generally vary in size.

If you want to save space (a lot of space...), you can compress the RAF files on your computer. If on a Mac or any other Unix machine, use the program 'bzip2' (in the terminal). You can save up to 80%, depending on the scene. There are likely similar compression tools on Windows.

If we assume lossless compression works as advertised, what's the benefit of uncompressed files? I would guess less pressure on the in-camera processor (and the Fuji's is feeble, it seems to me), but burns up cards and maybe would extend write times...

Anyone familiar with a workflow that would allow me to do that to my files that have already been imported to Lightroom?

I.e. any software that will loss-less compress all files in a directory and would the re-written files just work in Lightroom?

I don't think Lightroom reads compressed files. Probably the most common compression tool is gzip (creates files with extension '.gz'). It would be easy for any software to automatically recognize such files and uncompress them on the fly, but I don't think many programs have that ability. A lot of scientific software does.

What I would suggest is to compress the raw files for archival purposes, not for when you are actively working on them. I do that all the time, unless you have scripts set up that do the constant compressing/uncompressing for you. Compression tools can work on all files in a directory, but how exactly and what tools to use will depend on your operating system.